Under Michigan Residential Code, which statement about stair construction is correct?
Correct Answer
C) Maximum riser height is 7.75 inches, minimum tread depth is 10 inches
Michigan Residential Code specifies maximum riser height of 7.75 inches and minimum tread depth of 10 inches for residential stair construction.
Why This Is the Correct Answer
Option C is correct. The Michigan Residential Code (IRC R311.7) specifies that risers shall not exceed 7-3/4 inches (7.75 inches) in height and treads shall have a minimum depth of 10 inches. These are the standard IRC residential stair dimensions adopted by Michigan.
Why the Other Options Are Wrong
Option A: Maximum riser height is 8.25 inches, minimum tread depth is 9 inches
Maximum riser height of 8.25 inches and minimum tread depth of 9 inches is incorrect. These dimensions are too permissive—a riser of 8.25 inches exceeds the 7.75-inch code maximum, creating stairs that are too steep and unsafe. A 9-inch tread is also shallower than the 10-inch code minimum.
Option B: Maximum riser height is 8 inches, minimum tread depth is 9.5 inches
Maximum riser height of 8 inches and minimum tread depth of 9.5 inches is incorrect. An 8-inch riser exceeds the 7.75-inch maximum. A 9.5-inch tread is also below the 10-inch minimum. This option uses rounder numbers that might seem plausible but do not match the IRC/Michigan code.
Option D: Maximum riser height is 7.5 inches, minimum tread depth is 11 inches
Maximum riser height of 7.5 inches and minimum tread depth of 11 inches is incorrect. While 7.5 inches is more conservative than the maximum of 7.75 inches (and thus would be compliant for the riser), the tread depth of 11 inches exceeds the minimum. However, this option is wrong because it states parameters that do not match the code definition—the code maximum riser is 7.75", not 7.5". Exam questions ask for the code standard, not more conservative values.
Memory Technique
Remember: '7-3/4 up, 10 across.' The riser goes up (max 7.75"), the tread goes across (min 10"). Think of '7 and 10' as the key numbers, with the quarter-inch refinement on the riser: 7.75". You can also remember the rule that riser + tread should approximately equal 17-18 inches: 7.75 + 10 = 17.75 (within the ideal range).
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